The present invention relates to asphalt cement compositions for use in paving and roofing products and more particularly to powder additive compositions that can be added to asphalt cements to impart multigrade properties thereto.
Asphalt compositions are used in over 90 percent of the pavement surface applications in the United States. Natural asphalts obtained from lakebeds were utilized as early as 1874. Years later, rock asphalt deposits found in several southern and western states were pulverized, placed and rolled to form pavement surfaces. Since the early 1900""s, asphalts produced during the process of refining petroleum have dominated both paving and roofing applications.
Asphalt is a dark brown to black, highly viscous material containing bitumens as the principle constituent and is found in varying proportions in most crude petroleums. The asphaltic residuum from petroleum refining, substantially freed of lighter overhead fractions, is commonly called xe2x80x9casphalt.xe2x80x9d Paving asphalts are classified as asphalt cement, cutback asphalt and asphalt emulsions.
Asphalt cement is an asphalt having properties that are particularly suitable for pavement surface and roofing applications and specialty products. For road construction, asphalt is heated to a free flowing consistency and mixed with an aggregate heated to approximately the same temperature (usually 135xc2x0 C. to 160xc2x0 C.). The resulting mixture is placed on a prepared surface, compacted and cured to produce hot mix asphalt (HMA). In the long history of asphalt paving, the hot mix process of mixing asphalt cement and aggregate has remained the process of choice as offering the most favorable balance of cost and quality.
Asphalt cements used in paving applications today are graded according to stiffness at different temperatures before and after aging. The most common grading system in the United States is based on specifications from the Association of American Highway and Transportation Officials (AASHTO).
Superpave (superior performing pavements) refers to pavements that are made by a method of construction developed in the United States through research funded by AASHTO. Grading is based on high and low temperature stiffness of the asphalt binder under Superpave performance graded (PG) binder specification. A PG graded binder PG 64-22 would have a stiffness modulus of at least 1 Kilo Pascal (kPa) at 64xc2x0 C. This asphalt after short term and long term aging would also have a limiting stiffness of less than 300,000 kPa at xe2x88x9222xc2x0 C. over a 2 hour time period. The low temperature stiffness gives equivalent values at xe2x88x9212xc2x0 C. (10xc2x0 C. warmer) over 2 minutes and is the method used by AASHTO. Adding the two temperatures together for a given PG grade gives the temperature range over which the asphalt performs. For PG 64-22 the temperature spread would be 86xc2x0 C. This temperature spread is typical of a high quality unmodified paving asphalt cement. The PG grading system from AASHTO increases and decreases in grade in 6xc2x0 C. increments. To produce a PG 70-22 grade which would be the next high temperature grade in the specification without reducing the low temperature to xe2x88x9216xc2x0 C. is difficult with unmodified asphalt. Only a few asphalts can achieve the 92xc2x0 C. spread without modification. In order to increase spread most asphalt cement manufacturers have resorted to adding modifiers. Modification can be done by a number of methods including addition of polymers or chemicals.
Outside of the United States asphalts are generally graded by other methods such as penetration or viscosity. Penetration involves dropping a needle with 100 grams of mass into the asphalt cement at 25xc2x0 C. A soft asphalt will allow the needle to penetrate more deeply into the asphalt cement. Asphalts used in colder climates use softer grades and in warmer climates harder asphalts are used to avoid rutting of the pavement. Another grading system that is used is grading by viscosity. Asphalts cements are graded at 60xc2x0 C. using viscosity and at 25xc2x0 C. using penetration to characterize the asphalt at two temperatures. Roofing asphalts used in Build Up Roofs (BUR""s) for flat or sloped roofs are graded by penetration and softening point under the ASTM Method D312 international specification. Softening point is the temperature at which the asphalt first begins to soften and is an indication of flow temperature in roofs and some paving specifications. Generally asphalts with softer penetration and higher softening points would be considered as having a broader temperature range analogous to PG grades with broader temperature ranges of 92xc2x0 C. or greater, and again would contain modifiers to improve the temperature range for the asphalt to perform within.
Asphalt cements for paving applications must be selected with care based on the traffic loading, speed, and climate to which the pavement will be exposed. High traffic loading, low traffic speed and wide climate ranges require asphalts that have broad temperature requirements. The asphalt must have sufficient stiffness to resist flowing during excessive hot weather with slow moving trucks. It also must not crack on the coldest days of the year especially after many years of service. Pavements in more moderate climates with little traffic require much less of a temperature range and unmodified asphalts have shown historic performance in such applications.
In roofing asphalt, the roof location (climate) and slope of the roof are important considerations. Again, the asphalt must not soften too much on the hottest day of the year and cause the roof to slide or flow due to the slope of the roof. Minimum softening points have been found to be a good measure to assure against this happening. This is analogous to high temperature stiffness measurements in paving asphalts.
To avoid low temperature cracking in penetration graded asphalt cements, the material is evaluated for penetration at 25xc2x0 C. and 4xc2x0 C. with minimum values to insure that the asphalt does not reach its limiting stiffness of 300,000 kPa used in performance graded paving asphalt testing.
U.S. Pat. No. 4,874,432, assigned to Asphalt Materials, Inc. was developed to produce a xe2x80x9cmultigradexe2x80x9d or gelled asphalt cement having improved properties over conventional asphalt cements, including reduced temperature susceptibility and a lower age hardening rate. These improved properties were achieved using conventional hot-mix asphalt processes in existing hot-mix equipment, standard roofing application equipment and specialty asphalt application equipment.
The term multigrade asphalt was adopted by the assignee of U.S. Pat. No. 4,874,432 to describe a novel gelled asphalt cement having reduced temperature susceptibility and improved age hardening properties as compared to conventional asphalt cement. These improvements were accomplished by saponifying in the liquid asphalt, substantially free of water, at least one saponifiable organic acid and at least one resin acid with an alkali metal base, or by adding the already saponified product to the liquefied asphalt. The resulting gelled asphalt can be utilized in conventional processes in road, roofing and specialty applications.
Conventional asphalt cements have the Theological properties of viscous liquids when used at elevated temperatures in hot-mix processes. The asphalt remains a flowable liquid in accordance with its particular viscosity-temperature relationship, throughout its incorporation with aggregate and its laydown as an asphaltic concrete. In this physical state the asphalt is susceptible to flowing off the aggregate, depending on factors such as temperature, nature and surface area of the aggregate and the size and configuration of voids.
The inventors of U.S. Pat. No. 4,874,432 discovered that asphalt could be gelled by a direct saponification reaction requiring only a trace amount of an ionizing liquid to form an ionizing zone within the liquified asphalt where the saponification reaction can begin. Water produced as the reaction proceeds is sufficient to sustain a reaction that permeates the entire mix containing the asphalt and saponification ingredients.
Because of the qualitative advantages of gelled multigrade asphalt prepared according to U.S. Pat. No. 4,874,432, a paving asphalt grading as a PG 64-22 under Superpave can be upgraded to a PG 70-22. This allows a one grade improvement in high temperature properties without a loss of low temperature characteristics. In effect, asphalt cements manufactured in this manner impart a greater temperature range to the asphalt cement from an 86xc2x0 C. temperature spread to a 92xc2x0 C. spread. Similarly, this process improves the grading range using penetration viscosity and softening point range for paving and roofing asphalts.
Multigrade asphalt cement made by the process as described in U.S. Pat. No. 4,874,432 is a substantially water free material that is capable of being stored at a temperature of 120xc2x0 C. or higher without foaming and is suitable for shipping to end users for mixing with aggregate to produce asphaltic concrete by conventional hot-mix methods. It is also suitable for shipping to end users for conventional roofing and specialty applications.
The manufacture of multigrade asphalt cement is performed at regional facilities using processes such as described in U.S. Pat. No. 4,874,432. This multigrade asphalt cement is then transferred to HMA manufacturing facilities at other locations for the mixing with appropriate heated aggregates. The costs associated with the transport of the asphalt cement results in a geographical limitation on the ability to market multigrade asphaltic cement over a wide area due to shipping costs. In addition, the capital costs for the construction of multigrade asphalt cement manufacturing facilities limits the ability to fully utilize this high quality product at many locations around the world.
Heretofore multigrade asphalts have been produced by adding unreacted reactant components to liquid asphalt compositions, and allowing the reactant components to react together within the liquid asphalt composition media. The reaction products of the added reactant components produced in the liquid asphalt media interact with the components of the liquid asphalt composition and effect changes in the high and/or low temperature characteristics of the resulting liquid asphalts. One limitation on such a process is that the necessary liquid asphalt component which serves as the medium in which the added reactant components react, has a significant mass or bulk volume that creates handling difficulties and requires rather large processing equipment.
The present invention is directed to a composition that is the reaction product of certain reactant components that is produced by reacting the reactant components together outside of any asphalt media. The resulting reaction composition (referred to below as a multigrade additive) can subsequently be added to conventional asphalt cement compositions to produce multigrade asphalt cement products as described herebelow.
According to various features, characteristics and embodiments of the present invention which will become apparent as the description thereof proceeds, the present invention provides a multigrade powder additive composition which consists essentially of the reaction product of:
a) at least one saponifiable organic acid;
b) at least one resin acid;
c) at least one unsaturated organic compound; and
d) an alkali metal base,
wherein water is removed during the reaction so that the percentage of water in the final reaction product is from about 0.2 to about 1.5 wt. %.
The present invention further provides a method of making a multigrade powder additive composition which involves:
a) providing at least one saponifiable organic acid;
b) providing at least one resin acid;
c) providing at least one unsaturated organic compound; and
d) providing an alkali metal base,
e) combining the least one saponifiable organic acid, the at least one resin acid, the at least one unsaturated organic compounds, and the alkali metal base together to form a reaction mixture that undergoes a saponifying reaction;
f) removing water from the reaction mixture during the saponifying reaction; and
g) recovering the reaction product.
The present invention also provides a multigrade asphalt which includes:
a) a preformed reaction product of:
i) at least one saponifiable organic acid;
ii) at least one resin acid;
iii) at least one unsaturated organic compound; and
iv) an alkali metal base combined together with
b) an asphalt material.
The present invention further provides a method of making a multigrade asphalt which involves:
a) combining and reacting together:
i) at least one saponifiable organic acid;
ii) at least one resin acid;
iii) at least one unsaturated organic compound; and
iv) an alkali metal base; to form a reaction product; and
b) combining the reaction product with an asphalt material.